The present invention relates to an autorefrigeration process for the preparation of alpha-olefin polymers. More particularly the present invention relates to an improvement in the process of autorefrigeration which reduces fouling. In one aspect the invention relates to novel apparatus for use in autorefrigeration.
Autorefrigeration generally and in this invention relates to the vaporization of solvent-diluent medium from a liquid phase reaction thereby removing exothermic head of reaction and maintaining a substantially constant temperature in the medium remaining in solution. The vaporized solvent-diluent is usually recovered, for example in a condenser and recovered solvent-diluent is returned to the reactor.
There are a number of embodiments relating to autorefrigeration. In some embodiments, the solvent-diluent is a single material such as toluene, in other embodiments the solvent-diluent is a constant boiling azeotrope such as benzenecyclohexane. In other reactions the solvent-diluent which is vaporized, recovered, condensed, and returned to the reactor, is either the reactant or one of the reactants in the system. This latter embodiment is of particular interest in regard to the polymerization of alpha-olefins. In any autorefrigeration, temperature control requires a vapor space in the reaction vessel into which the vaporized solvent-diluent medium expands. One of the common difficulties in autorefrigeration has been the fouling of the reactor at the vapor-liquid interface in the case of the polymerization reaction, and also the fouling of the condenser because the entrained material carried overhead with the vaporized solvent-diluent.
It is a feature of the present invention that autorefrigeration reactions carried on according hereto, are able to be carried out for periods substantially along than the prior art method and processes, before fouling requires the shut down and the clean up of the reactor and related equipment.
It is a particular feature of the present invention that a particular method of returning the recovered and cooled solvent-diluent to the reactor and to the reaction medium has been discovered, which result in substantially reduced fouling of the system.